TUNGSTEN (soluble and insoluble): METHOD 7074, Issue 2, dated 15 August 1994 - Page 3 of 3 CALIBRATION AND QUALITY CONTROL: 15.
16.
Calibrate with at least six working standards over the range 0.05 to 12 mg W per sample. a. Add known amounts of calibration stock solution to 100-mL volumetric flasks containing 10 mL 0.5 M NaOH and 10 mL 20% Na 2SO 4; dilute to volume with distilled, deionized water. b. Analyze together with samples and blanks (steps 17 through 19). c. Prepare calibration graph (absorbance vs. solution concentration, µg/mL). Analyze three quality control blind spikes and three analyst spikes to ensure that the recovery and calibration graph are in control (steps 6 through 14 and 17 through 19).
MEASUREMENT: 17. 18. 19.
Set spectrophotometer to conditions on page 7074-1. Aspirate standards and samples. Record absorbance readings. If the absorbance values for the samples are outside of the range of the standards, dilute the solutions with 0.05 M NaOH/2% Na 2SO 4 solution, reanalyze, and use the appropriate dilution factor in calculations.
CALCULATIONS: 20. 21.
Determine the solution concentrations of tungsten in the sample, C s (µg/mL), and average media blank, C b (µg/mL), from the calibration graph. Using the solution volumes, mL of the sample (V s) and media blank (V b), calculate the concentration of tungsten, C (mg/m 3), in the air volume sampled, V (L):
EVALUATION OF METHOD: This method is based on P&CAM 271 [3,4] and was further evaluated and ruggedized under contract [1]. Laboratory testing with spiked samples over the ranges of 0.17 to 0.8 mg per sample (soluble) and 0.34 to 7.9 mg per sample (insoluble) gave precisions ( Sr) of 0.079 (soluble) and 0.076 (insoluble) [1]. Both soluble and insoluble tungsten species collected on filters were stable for two weeks [1]. REFERENCES: [1]
[2] [3] [4]
Carlin, L. M., G. Colovos, D. Garland, M. Jamin, M. Klenck, T. Long, and C. Nelson. Analytical Methods Evaluation and Validation: Arsenic, Nickel, Tungsten, Vanadium, Talc and Wood Dust, NIOSH Contract No. 210-79-0060 (1981), available as Order No. PB 83-155325 from NTIS, Springfield, VA 22161. User check, UBTL, Inc., NIOSH Sequence #4213-M (unpublished, May 23, 1984). NIOSH Manual of Analytical Methods, 2nd ed., Vol. 4, P&CAM 271, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 78-175 (1978). Hull, R. D. Analysis of Tungsten by Atomic Absorption Spectrophotometry: A Feasibility Study, NIOSH, DPSE, MRB, IMDS Technical Report (unpublished, December, 1977).
METHOD WRITTEN BY: R. DeLon Hull, Ph.D., NIOSH/DBBS; additional data obtained under NIOSH Contract 210-79-0060.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
